This invention pertains to rotary electrical variable resistors.
Various rotary electrical variable resistors have been known.
Very early in electrical apparatus bronze switch points were connected to bobbins of resistance wire and a bronze switch arm was arranged to sweep over the switch points, which were arranged in a circle.
Later, uniform circular graphitic resistive elements were directly swept over by a switch arm.
A linear adaption of this technique is disclosed in Kock et al, U.S. Pat. No. 2,215,124, in which sliding metal fingers contact two resistor areas on a substrate, in order to give "thumpless" electric organ keying.
Keranen, in U.S. Pat. No. 3,805,209, discloses resistive elements that are fired on a substrate, but these are parts that play no active role with a switch structure. They are in coaxial attenuators that are switched as a whole in or out of a microwave coaxial transmission line.
Basket, in U.S. Pat. No. 3,448,427, discloses several related wafer resistor structures having a fixed resistor element and a companion resistor element that can be varied in resistance value by rotating one part of the structure with respect to another part.
Eyelets are used for through-wafer electrical connections. Pins may be soldered to contacts on the printed circuit board (PCB) upon which the device is mounted.
The resistive and conductive paths are essentially special-purpose and do not suggest the universal arrangement provided by the subject invention.
Immediately prior printed circuit board technique of the present inventors has placed grouped resistors away from the rotary contacts as the only way of accomplishing such a structure. This structure required a large number of relatively very long conductive paths from the resistors to the contacts and a very difficult printed circuit layout.